JD 6210 three point hitch problem

I have a 1999 model 6210 w/o a cab. I bought it at an auction and knew that the 3 pt hitch was not working. My mechanic tells me that the Hitch Control unit is bad. It is corroded inside and appears to have been wet. He said that this is a recurring problem.

It has a 640 FEL that works fine.

I don't mind spending the money to fix it (as I said, I knew it had a problem).

I am wondering if this really is a recurring problem, is there a fix to prevent a reoccurrence?

Any input would be appreciated.

Thanks.